Performance Study of MEMS Piezoresistive Pressure Sensors at Elevated Temperatures

Three types of piezoresistive pressure sensors were designed and fabricated using different process technologies incorporating standard diffused piezoresistors, and oxide isolated polysilicon or single crystal silicon piezoresistors. The performance of these sensors up to an elevated temperature of 200 degrees C and pressure of 140 bar was investigated by measuring the variation of sensitivity, offset voltage and hysteresis. At room temperature, the diffused piezoresistor based pressure sensor demonstrated sensitivity of 0.147 mV/V/bar and it was observed to operate up to the maximum temperature of 100 degrees C. The oxide isolated single crystal silicon piezoresistor and polysilicon piezoresistor based pressure sensors showed sensitivities of 0.211 mV/V/bar and 0.308 mV/V/bar respectively at room temperatures. These sensors could be operated up to the measured temperature of 200 degrees C without any failure. All types of sensors showed decreased sensitivities with temperature. With respect to the sensitivity at room temperature, the sensor with diffused piezoresistors exhibited 13% decrease of sensitivity at 100 degrees C. For oxide isolated single crystal silicon or poly silicon piezoresistors, the decrease in the sensitivity at 200 degrees C was 19.5% and 9.0% respectively y. At elevated temperatures of 200 degrees C, the sensors with oxide isolated polysilicon piezoresistors demonstrated the best performance in terms of lowest decrease of sensitivity, and variation of offset voltage and hysteresis.